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          【C#】再谈委托
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        <p><a target="_blank" rel="noopener" href="http://47.94.231.166/wp-content/uploads/2018/11/Delegate.html">>无扰阅读模式（测试）</a> 先报一下现况吧：目前正在做WPF版的Walkman Playlist Tools，增加和完善了很多功能，小小地图透一下： <a target="_blank" rel="noopener" href="http://upane.cn/archives/874/devenv_2018-11-09_22-26-03"><img src="http://47.94.231.166/wp-content/uploads/2018/11/devenv_2018-11-09_22-26-03-1024x555.png" alt=""></a> 具体改了什么功能，先卖个关子。 这么长时间没更真的没有在摸鱼哦！真的没有！  <a target="_blank" rel="noopener" href="http://upane.cn/archives/220/attachment/55"><img src="http://47.94.231.166/wp-content/uploads/2018/04/55.png" alt=""></a> 那么，我们步入正题吧：<br><a id="more"></a></p>
<h1 id="委托"><a href="#委托" class="headerlink" title="委托"></a>委托</h1><p>[delegate]</p>
<hr>
<h6 id="委托？"><a href="#委托？" class="headerlink" title="委托？"></a>委托？</h6><blockquote>
<p>简单地说，委托的实质是函数的指针。</p>
</blockquote>
<h6 id="实现委托？"><a href="#实现委托？" class="headerlink" title="实现委托？"></a>实现委托？</h6><blockquote>
<p>和其他类型一样，委托在实现之前也要先定义类，这个类称为委托，而委托函数的是委托的成员（可以看作委托类的对象）。</p>
</blockquote>
<h2 id="①Action委托"><a href="#①Action委托" class="headerlink" title="①Action委托"></a>①Action委托</h2><p>前面说过，委托在实现之前必先定义类，这个类可以自己定义（之后会讲），也可以直接使用系统定义好的委托类，这里讲的<code>Action</code>和下面的<code>Func</code>就是这样的类。 <code>Action</code>委托是可添加<strong>无传入值，且无返回值（<code>void</code>）方法</strong>的委托类。</p>
<h4 id="创建："><a href="#创建：" class="headerlink" title="创建："></a>创建：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">Action anyname =<span class="keyword">new</span> Action( FunctionHere );</span><br></pre></td></tr></table></figure>
<h4 id="调用（以下三条代码效果相同）："><a href="#调用（以下三条代码效果相同）：" class="headerlink" title="调用（以下三条代码效果相同）："></a>调用（以下三条代码效果相同）：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">anyname.Invoke();<span class="comment">//调用委托（完全版）</span></span><br><span class="line">anyname();<span class="comment">//调用委托（简写版）</span></span><br><span class="line">FunctionHere();<span class="comment">//原函数</span></span><br></pre></td></tr></table></figure>
<h2 id="②Func委托"><a href="#②Func委托" class="headerlink" title="②Func委托"></a>②Func委托</h2><p>Func委托是通过泛型容纳任何一种函数的委托类。</p>
<h4 id="创建：-1"><a href="#创建：-1" class="headerlink" title="创建："></a>创建：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">Func&lt;Type1,Type2,...ReturnType&gt; anyname=<span class="keyword">new</span> Func&lt;Type1,Type2,...ReturnType&gt;( FunctionHere )</span><br></pre></td></tr></table></figure>
<p>如上，泛型中可填入任意数量的数据类型，其中最后一个输入的数据类型用作规定函数的返回类型，其他（除了最后一个）数据类型可以规定函数的传入类型。需要注意的是，若只填入一个类型，那么这个类型是函数的返回类型。</p>
<h4 id="调用："><a href="#调用：" class="headerlink" title="调用："></a>调用：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">anyname.Invoke();<span class="comment">//调用委托（完全版）</span></span><br><span class="line">anyname();<span class="comment">//调用委托（简写版）</span></span><br><span class="line">FunctionHere();<span class="comment">//原函数</span></span><br></pre></td></tr></table></figure>
<h2 id="③委托的声明（自定义委托）"><a href="#③委托的声明（自定义委托）" class="headerlink" title="③委托的声明（自定义委托）"></a>③委托的声明（自定义委托）</h2><p>委托的声明方式与一般类不同，主要是为了照顾可读性和C、C++传统。 注意声明委托的位置，避免写错地方结果声明成嵌套类型。 委托所封装的方法必须类型兼容。</p>
<h4 id="定义："><a href="#定义：" class="headerlink" title="定义："></a>定义：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="built_in">delegate</span> <span class="built_in">double</span> <span class="title">Calc</span>(<span class="params">doule x,<span class="built_in">double</span> y</span>)</span>;</span><br><span class="line"><span class="keyword">class</span> <span class="title">Program</span></span><br><span class="line">&#123;</span><br><span class="line">   Calc calc1=<span class="keyword">new</span> Calc( FunctionHere );</span><br><span class="line">   ......</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h4 id="调用：-1"><a href="#调用：-1" class="headerlink" title="调用："></a>调用：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">calc1.Invoke((<span class="built_in">double</span>)<span class="keyword">var</span>,(<span class="built_in">double</span>)<span class="keyword">var</span>);<span class="comment">//调用委托（完全版）</span></span><br><span class="line">calc2((<span class="built_in">double</span>)<span class="keyword">var</span>,(<span class="built_in">double</span>)<span class="keyword">var</span>);<span class="comment">//调用委托（简写版）</span></span><br><span class="line">FunctionHere((<span class="built_in">double</span>)<span class="keyword">var</span>,(<span class="built_in">double</span>)<span class="keyword">var</span>);<span class="comment">//原函数</span></span><br></pre></td></tr></table></figure>
<h2 id="④委托的使用"><a href="#④委托的使用" class="headerlink" title="④委托的使用"></a>④委托的使用</h2><blockquote>
<p>——当作数据传入函数</p>
</blockquote>
<ul>
<li>用作模板（常位于代码中部，有返回值）</li>
<li>回调方法（常位于代码尾部，无返回值，多用于执行后续操作）</li>
</ul>
<p>注意：难精通、易使用、功能性强的功能一旦滥用后果非常严重 1. 这是一种方法级别的紧耦合，现实工作中使用应慎之又慎 1. 可使得程序可读性下降，doubug难度增加 1. 把委托回调、异步调用和多线程纠缠在一起，会让代码变得难以阅读和维护 1. 使用不当可能造成内存泄漏和程序性能下降</p>
<h2 id="⑤多播委托"><a href="#⑤多播委托" class="headerlink" title="⑤多播委托"></a>⑤多播委托</h2><p>刚刚演示的委托均为单播委托，即一个委托只有一个方法相应。由此推广，多播委托即为一个委托可有多个方法相应。</p>
<h4 id="方法："><a href="#方法：" class="headerlink" title="方法："></a>方法：</h4><p>使用<code>+=</code>可在委托的成员中再添加一个方法。</p>
<h4 id="演示："><a href="#演示：" class="headerlink" title="演示："></a>演示：</h4><figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">Action action1=<span class="keyword">new</span> Action(Function1);</span><br><span class="line">Action action2=<span class="keyword">new</span> Action(Function2);</span><br><span class="line">Action action3=<span class="keyword">new</span> Action(Function3);</span><br><span class="line">action1+=action2;</span><br><span class="line">action1+=action3;</span><br><span class="line">action1.Invoke();</span><br><span class="line"><span class="comment">/*效果与分别调用相同：</span></span><br><span class="line"><span class="comment">action1.Invoke();</span></span><br><span class="line"><span class="comment">action2.Invoke();</span></span><br><span class="line"><span class="comment">action3.Invoke();*/</span></span><br></pre></td></tr></table></figure>
<h2 id="⑥异步调用"><a href="#⑥异步调用" class="headerlink" title="⑥异步调用"></a>⑥异步调用</h2><p>先明确几个称呼： 一个程序只有一个<strong>进程</strong>，但是可以有很多个<strong>线程</strong>。</p>
<blockquote>
<p>同步=串行=单线程； 异步=并行=多线程；</p>
</blockquote>
<ul>
<li>直接同步调用：使用方法名</li>
<li>间接同步调用：使用单播/多播委托的<code>Invoke</code>方法</li>
<li>隐式异步调用：使用委托的<code>BeginInvoke</code>方法，如 <code>csharp anyname.BeginInvoke(delegate,object) //第一个传入值为委托类型，标明该线程做完后做什么，什么都不做就填null //第二个传入值默认传入null</code> 需要注意的是，这是相比主线程而分离的分支线程，也就是说使用n次<code>BeginInvoke</code>就调用了 <strong>n+1</strong>个线程</li>
<li>显式异步调用： 1.Thread类：</li>
</ul>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">Using System.Threading;</span><br><span class="line">Thread thread1=<span class="keyword">new</span> Thread(<span class="keyword">new</span> ThreadStart(Function1));</span><br><span class="line">Thread thread2=<span class="keyword">new</span> Thread(<span class="keyword">new</span> ThreadStart(Function2));</span><br><span class="line">Thread thread3=<span class="keyword">new</span> Thread(<span class="keyword">new</span> ThreadStart(Function3));</span><br><span class="line"><span class="comment">//创建了三个线程，共四个线程。</span></span><br><span class="line">thread1.Start();</span><br><span class="line">thread2.Start();</span><br><span class="line">thread3.Start();</span><br><span class="line"><span class="comment">//分别启动线程</span></span><br></pre></td></tr></table></figure>
<p>2.Task类：</p>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">Using System.Threading.Task;</span><br><span class="line">Task task1=<span class="keyword">new</span> Task(<span class="keyword">new</span> Action(Function1));</span><br><span class="line">Task task2=<span class="keyword">new</span> Task(<span class="keyword">new</span> Action(Function2));</span><br><span class="line">Task task3=<span class="keyword">new</span> Task(<span class="keyword">new</span> Action(Function3));</span><br><span class="line"><span class="comment">//注意这里给Task的构造方法传入值的其实是个委托</span></span><br><span class="line">thread1.Start(); </span><br><span class="line">thread2.Start(); </span><br><span class="line">thread3.Start(); </span><br><span class="line"><span class="comment">//分别启动线程</span></span><br></pre></td></tr></table></figure>
<h2 id="⑦用接口代替委托"><a href="#⑦用接口代替委托" class="headerlink" title="⑦用接口代替委托"></a>⑦用接口代替委托</h2><p>Java的做法，降低耦合度，提高可读性</p>

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